The present disclosure relates to a memory element storing information based on any change of electrical characteristics observed in a memory layer including an ion source layer and a resistance change layer, to a method of manufacturing the same, and to a memory device.
A semiconductor nonvolatile memory popularly used for data storage has been a NOR or NAND flash memory. As for such a semiconductor nonvolatile memory, many attempts have been made to increase the capacity thereof by the microfabrication of memory elements and drive transistors therein. However, the semiconductor nonvolatile memory has been pointed out that there are limitations on microfabrication considering the expectation for a high level of voltage for writing and erasing, and the limited number of electrons to be injected into a floating gate.
For overcoming such limitations on microfabrication, a next-generation nonvolatile memory currently proposed is a ReRAM (Resistance Random Access Memory) or a PRAM (Phase-Change Random Access Memory), for example (for example, see Waser et. al., Advanced Materials, 21, p 2932 (2009), and Japanese Unexamined Patent Application Publication No. 2006-196537. These memories are each in the simple structure including a resistance change layer between two electrodes. In the memory of Japanese Unexamined Patent Application Publication No. 2006-196537, as an alternative to the resistance change layer, an ion source layer and an oxide film (thin film for storage) are provided between first and second electrodes. In these resistance change memories, a conductive path is formed through migration of atoms or ions by heat or an electric field, whereby a resistance value is supposed to change.
The resistance change memory described above is provided with an ion source layer, which contains elements of aluminum (Al), copper (Cu), zirconium (Zr), tellurium (Te), or others. For forming such an ion source layer containing the elements as above, an option is to form a mixture film of a homogeneous component by co-sputtering or using any alloy target, or to form a multi-layer film by forming films of individual elements. Forming a multi-layer film has an advantage of being able to form an ion source layer with the favorable operation performance even if a film-forming device in use is not capable of co-sputtering, for example.